VFDs and pump motors

We have a pit pump connected to a VFD and an ultrasonic sensor ramps up/down the VFD in turn increases/decreases motor hz for liquid level. The VFD is set to start at 10Hz (low level)and max out at 60hz(high level). The problem we are having is the motor trips out at 45hz. Any thoughts as to the problem? Could the electricians mistakenly wired for 230v instead of 460v causing the issue?

if they do that it would not trip because of current (i assume that as most usual as you did not specify the trip), it would result in lower flow rate. (and maybe undervoltage trip)

Overload trips when pump #3 is running at over 45 hz.
We switched the #3 motor leads from #3 inverter to #2 inverter and the #2 overload trips.
Overload is set at 5.1 amps
We are unable to observe any peak loads on our amp meter. Amps observed to fluctuate from 3.8 to 4.2 amps at 60 hz.

if motor is normal 5 amps and it trips at 45 Hz it is wrong voltage so get it out of the pit and check the wiring.

Dheiden23,

Welcome to the forum!

I do not know if any of the other forum members are having any difficulty following this thread, but cannot tell from this next quote if you mean that the motor is connected for 230V or if the VFD is connected to a 230V supply or (very remote possibility) if the VFD is programmed to deliver 230V at 60 Hz.

Dheiden23 said:

The problem we are having is the motor trips out at 45hz. Any thoughts as to the problem? Could the electricians mistakenly wired for 230v instead of 460v causing the issue?

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This next quote is also not clear to me (it might be just me and not every one else). I cannot tell if you have overload(s) separate from the VFD or if you are meaning that the VFD faults on motor overload. It also makes me curious if motor #3 and motor #2 are the same size and voltage. If you do have separate overloads are they the same on setup #3 and setup #2? You also do not mention if you moved the programing from inverter #3 to #2 when you performed this test.

Dheiden23 said:

Overload trips when pump #3 is running at over 45 hz.
We switched the #3 motor leads from #3 inverter to #2 inverter and the #2 overload trips.

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It is a well known fact that a conventional ammeter cannot measure VFD controlled motor amps with any accuracy. Conventional wisdom is to use the VFD display to observe the motor amps.

Dheiden23 said:

Overload is set at 5.1 amps
We are unable to observe any peak loads on our amp meter. Amps observed to fluctuate from 3.8 to 4.2 amps at 60 hz.

Click to expand...

I'm also curious if the pumps are submersible sump pumps?

Any changes to the system? Or is it a new install?

Has a meggar test been performed on the suspect motor (with VFD disconnected)?

I feel that a better description of your system would help us to understand what might be wrong. Things like VFD model, one VFD or 3, VFD programming and fault codes would also help.

welcome,

I also agree with milldrone.

please detail your application.
plant voltage and motor voltage
size of vfd, brand, model #
number of motors used, number of vfd's, size of overloads, and the size of each.
is each motor vfd rated?
state of the vfd and what process was used when stitching motors.

I was able to follow and offer suggestions until I saw the post about pump #3.

please clarify so we can offer suggestions.

regards,
james

Are your pump motors rated for VFD use?? Most pumps aren't, but people connect them up to VFD's anyway!
It is quite possible that the windings in that motor break down as the frequency increases.

Using a drive on a pump can be a problem when you go to retrofitting a drive to a pump that used motor starters. At 45 hz your motor torque available may not be enough to drive the pump and that will cause the drive to fail on overload. Check the motor torque curve and pump torque curve for the ones you have. I have seen this before in the past, and at about 45 hz. I'm not saying that this is your problem but it may be the root cause.

Another thing to check, is back in the day, motors would be wired for 230 Vac then hooked to a drive with a volts per hertz curve of 0-0 , 60-230 and 120-480 (hz-volts) to effectively keep the torque constant which is what a pump needs. Since the motor was rated at 480 volts already this allows you to use it this way. The only problem with it is the motor must be able to handle the higher RPM and the drive has to be rated at double the current of the motor. (the motor will draw the 230 name plate amps).

mendonsy said:

Are your pump motors rated for VFD use?? Most pumps aren't, but people connect them up to VFD's anyway!

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I would find that rather odd as pumps have parabolic torque curve and thus ideal for starting with low torque and for operating at smaller rpms to save energy.
almost all pumps in our water distribution system is VFD controlled, and those that are not are filling backup reservoirs. (no need for them, they have softstarters)

also pumps can have problems with starting on open valves (open pipeline). if this happens at startup try starting on closed valve.

balash said:

I would find that rather odd as pumps have parabolic torque curve and thus ideal for starting with low torque and for operating at smaller rpms to save energy.
almost all pumps in our water distribution system is VFD controlled, and those that are not are filling backup reservoirs. (no need for them, they have softstarters)

also pumps can have problems with starting on open valves (open pipeline). if this happens at startup try starting on closed valve.

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It has nothing to do with the characteristics of the pump and using a VFD to ramp a pump up to speed is fine IF the motor windings are rated for the VFD voltage. The peak voltage out of a 480 volt VFD is typically a bit over 700 volts. VFD rated motor windings can handle that peak but many other motors cannot.
If your pumps were ordered with motors for VFD duty they will be fine, but if not the windings could eventually break down from high voltage.

mendonsy said:

It has nothing to do with the characteristics of the pump and using a VFD to ramp a pump up to speed is fine IF the motor windings are rated for the VFD voltage. The peak voltage out of a 480 volt VFD is typically a bit over 700 volts. VFD rated motor windings can handle that peak but many other motors cannot.
If your pumps were ordered with motors for VFD duty they will be fine, but if not the windings could eventually break down from high voltage.

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you are absolutely correct!!

And just when is "eventually"?

My experience tells me that internal winding failure due to "non-vfd rated" motors is very...very...very unlikely.

Unless you are the vfd technical support person for a major VFD manufacturer, in which case the 1 in 10,000 customer with a failure will call and ask "what's up"?

The windings for a 600V motor are not materially different than those for a 200V motor.H

In any case, motor design is NOT the reason that a VFD would kick out at 45 hz.

Lets put on our thinking caps..

CalG said:

My experience tells me that internal winding failure due to "non-vfd rated" motors is very...very...very unlikely.

Unless you are the vfd technical support person for a major VFD manufacturer, in which case the 1 in 10,000 customer with a failure will call and ask "what's up"?

The windings for a 600V motor are not materially different than those for a 200V motor.H

In any case, motor design is NOT the reason that a VFD would kick out at 45 hz.

Lets put on our thinking caps..

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I was an ABB drive rep for 12 years, I have seen a lot of motor failures due to switching from a contactor to a drive, and not changing the motor..... There is more to an inverter duty motor than just insulation. The windings are better secured, insulated for higher voltages, and the coils will have better thermal transfer to the outside. The rotors are also built to withstand higher temperatures and velocities. All laminations in the motor are also designed to reduce eddy currents and for higher values of saturation.

Yes you can run most standard motors with an inverter without problems, but almost every standard motor will fail at some time when using an inverter and taking the motor to it's maximum performance.

try running a standard duty 10HP motor, at it's rated load and current at 10Hz and 90% duty factor, and I can guarantee failure almost every time unless you make motor modifications.

Some pump/motor combinations work because the time period which the motor gets to "synchronous" speed using a contactor. Using a drive on the same motor, and either not getting to synchronous speed (running at less than synchronous) or just taking a lot longer time to reach synchronous speed can cause motor failure or drive faults. I have seen 5 hp to 250hp motor/pump combinations that worked for 30 years with contactors fail as soon as a drive was used to replace the contactor. WHat we usualy found was at some point the motor torque was close or just below the torque needed to run that pump at that particular speed. (remember during start up a motor will draw up to 500% nameplate to overcome a load, but on a drive it is limited to 100-200% and may not make the load rotate!)

What type of fault is the VFD reporting?

James Mcquade said:

welcome,

I also agree with milldrone.

please detail your application.
plant voltage and motor voltage
size of vfd, brand, model #
number of motors used, number of vfd's, size of overloads, and the size of each.
is each motor vfd rated?
state of the vfd and what process was used when stitching motors.

I was able to follow and offer suggestions until I saw the post about pump #3.

please clarify so we can offer suggestions.

regards,
james

Click to expand...

ADD to list
rated HP of motor
whether checked to see if motor and pump have any mechanical issues
What does pump curve look like